1. Field of the Invention
This invention relates to transfer switches and, more particularly, to transfer switches for selectively feeding power from one of two input lines to a load.
2. Background Information
Transfer switches are known in the art. See, for example, U.S. Pat. No. 5,397,868.
Transfer switches operate, for example, to transfer a power-consuming load from a circuit with a normal power supply to a circuit with an auxiliary power supply. Applications for transfer switches include stand-by applications, among others, in which the auxiliary power supply stands-by if the normal power supply should fail.
A transfer switch typically comprises a pair of circuit interrupters combined with a drive input and a linkage system. The preferred types of circuit interrupters have been molded-case switches and molded-case circuit breakers because these types are commercially available in a wide array of sizes and are relatively economical compared to other options. The preferred type of drive input depends on the application for the transfer switch. Usually motors are preferred, but at other times there is a clear preference for manually operated mechanisms.
In most residential and commercial buildings, the electrical wiring is only fed by a utility power source. In order to have a backup power source, such as a generator or inverter, it is necessary to provide a separate electrical back-up panel and, also, to re-wire the original panel. The cost of rewiring and the separate backup panel is great.
Accordingly, there is room for improvement in transfer switches.
These needs and others are met by the present invention, which provides a transfer switch that fits into existing circuit breaker panels without excessive wiring. The circuit breaker, which fits into existing electrical panels, has connections to allow such circuit breaker to supply the load with either a utility power source or a backup power source.
According to one aspect of the invention, a transfer switch comprises: a circuit breaker housing; a first line terminal; a second line terminal; a load terminal; a transfer arm adapted to move between a first position in which the transfer arm is electrically connected to the first line terminal and a second position in which the transfer arm is electrically connected to the second line terminal; means for moving the transfer arm between the first and second positions thereof; separable contacts electrically connected between the transfer arm and the load terminal; and an operating mechanism for opening and closing the separable contacts.
The housing may include a pivot point, and the transfer arm may include a first end, a second end and a pivot therebetween. The pivot pivotally engages the pivot point of the housing and is adapted to pivot the transfer arm between the first and second positions thereof. The means for moving the transfer arm may include a solenoid having a plunger, which engages the transfer arm between the pivot and one of the first and second ends thereof.
The housing may include a pivot point, and the transfer arm may include a first end, a second end and an intermediate portion therebetween. The first end has a pivot adapted for movement of the transfer arm between the first and second positions thereof, the second end has a first contact adapted for electrical connection with the first line terminal in the first position of the transfer arm and a second contact adapted for electrical connection with the second line terminal in the second position of the transfer arm. The intermediate portion of the transfer arm is adapted for movement by the means for moving the transfer arm. The means for moving the transfer arm may include a solenoid having a plunger which engages the transfer arm at the intermediate portion thereof.
As another aspect of the invention, a remotely controllable transfer switch comprises: a circuit breaker housing; a first line terminal; a second line terminal; a load terminal; a transfer arm adapted to pivot between a first position in which the transfer arm is electrically connected to the first line terminal and a second position in which the transfer arm is electrically connected to the second line terminal; a solenoid having a first coil, a second coil and a plunger engaging the transfer arm; a control circuit for the solenoid including a first terminal adapted to receive a first external signal, a second terminal adapted to receive a second external signal, and a third terminal adapted to receive a control voltage, the control circuit responsive to the first external signal to energize the first coil with the control voltage in order to move the plunger in a first direction to pivot the transfer arm to the first position thereof, the control circuit responsive to the second external signal to energize the second coil with the control voltage in order to move the plunger in a second direction to pivot the transfer arm to the second position thereof; separable contacts electrically connected between the transfer arm and the load terminal; and an operating mechanism for opening and closing the separable contacts.
The control circuit may further include a micro-switch having a normally open contact electrically connected in series with the first coil, a normally closed contact electrically connected in series with the second coil, and an operating member for switching the normally open contact and the normally closed contact. The normally closed contact and the normally open contact have a common terminal adapted to receive a control voltage to energize one of the first and second coils. The plunger of the solenoid has a projection which engages and actuates the operating member in the first position of the transfer arm, thereby causing the normally closed contact to open and the normally open contact to close.
The first terminal may be adapted for electrical connection with a first remote contact, which is referenced to a return of the control voltage. The second terminal may be adapted for electrical connection with a second remote contact, which is referenced to the return of the control voltage.